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A023814
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Number of associative binary operations on an n-set; number of labeled semigroups.
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12
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..9.
A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023, 2013.
C. Noebauer, Home page [broken link]
C. Noebauer, The Numbers of Small Rings
C. Noebauer, Thesis on the enumeration of near-rings
Eric Postpischil Posting to sci.math newsgroup, May 21 1990
Eric Weisstein's World of Mathematics, Semigroup.
Index entries for sequences related to semigroups
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CROSSREFS
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Cf. A001423, A001426, A023813, A023815, A027851.
a(n)+A079172(n)=A002489(n)
Sequence in context: A072402 A092084 A099715 * A217772 A062126 A222520
Adjacent sequences: A023811 A023812 A023813 * A023815 A023816 A023817
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KEYWORD
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nonn
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AUTHOR
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Lyle Ramshaw (ramshaw(AT)pa.dec.com)
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EXTENSIONS
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a(8), a(9) from Distler and Kelsey (2013). - N. J. A. Sloane, Feb 19 2013
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STATUS
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approved
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